1. Field of the Invention
The present invention relates to an improvement to a wheelchair, particularly a wheelchair utilized for racing purposes, and to a wheel centering mechanism for the front wheels of a wheelchair.
2. Description of the Prior Art
At present, most conventional wheelchairs are constructed with large rear wheels mounted in parallel, spaced fashion to support a frame and a seat thereon, and a pair of smaller, front wheels which also support the frame from beneath. The rear wheels of conventional wheelchairs are equipped with large, circular driving handwheels thereon, by means of which the wheelchair occupant manually propels the wheelchair. The front wheels of a conventional wheelchair are typically mounted independently of each other upon free-wheeling casters.
Conventional wheelchairs are typically steered by the occupant by means of the handwheels on the rear wheels. That is, when the wheelchair occupant wishes to turn to the right, a greater forward driving force is exerted on the driving handwheel of the left rear wheel than on the right rear wheel. Indeed, for a sharp right turn approaching a pivoting action a rearward driving force may be exerted on the handwheel of the right rear wheel while a forward driving force is exerted on the handwheel of the left rear wheel. To execute a left turn, the foregoing forces are reversed.
With front wheels independently attached to the frame by means of casters the wheelchair occupant has enhanced maneuverability and can execute extremely sharp turns. The front wheels, and the casters upon which they are mounted can be turned and twisted independently of each other, and the front wheels are not always disposed in mutually parallel relationship.
While conventional wheelchairs constructed as heretofore described are designed to maximize maneuverability and mobility for disabled persons, the very features which provide a high degree of maneuverability create considerable problems when wheelchairs are used for special purposes. Specifically, in recent years disabled persons have gained increasing interest in physical activities in which wheelchairs are propelled at high speeds. For example, although most major marathon races, were initially open only to persons running on foot, they now include a wheelchair division in which disabled persons may race in wheelchairs. Also, the sport of basketball has gained increased popularity to teams whose members must use wheelchairs.
When conventional wheelchairs are operated at high speeds, they tend to become unstable, particularly when they are turned. In marathon or other long distance wheelchair racing the front wheels of a wheelchair, in particular, experience a lack of stability. Conventional, caster mounted front wheels tend to vibrate and shimmy when a wheelchair is operated at a substantial speed, such as in competitive wheelchair racing. This condition becomes particularly dangerous during turning maneuvers executed at high speed, even if the turning radius is quite large. In conventional wheelchairs which employ front wheel casters, it is possible for one of the casters to twist sharply relative to the other, since the front wheels are mounted for orientation independently of each other. When this occurs, the wheelchair can turn over, and the occupant can be thrown to the ground. Even in the absence of such a disasterous twisting of a front wheel, the design of conventional wheelchairs creates problems when those chairs are operated at high speeds. The wheelchair occupant must combat the vibration and shimmying of the front wheels with intense concentration to ensure that driving power is appled equally to the driving handwheels of the wheelchair. Also, the vibration and shimmying of the front wheels creates a finite drag on the forward progress of the wheelchair, which must be overcome with additional driving force. As a result, the wheelchair occupant is thereby unnecessarily slowed and fatigued with operating a conventional wheelchair in racing or in some other athletic or high speed activity.